I have a 1994 626, 140K miles, original transmission, runs gret and shifts fine.
3 problems:
1. Hold light is flashing
2. OD light does not come on
3. Button on shifter does not appear to be activating anything.

Any suggestions?

Hope I can help. Is it a V6 or 4cyl? Many shops can tell you if there is a code in the system, when that light has been on. Can you actually feel it shift into O/D? Bad news is that most of the time when that light flashes, there is a serious fault inside the transmission. Don't jump to any conclusions until you check the code, though. Dealers are usually the best to make recommendation depending on what the code is. Be careful of independent shops in this case. I've see people get transmission repaired/rebuild in these cars, and get no further ahead. Just a drain on the wallet. Let me know how you make out!